Comparison between the intravenous and esophageal-gastric administration of glycerol in changing cochlear blood flow and serum osmolarity in the guinea pig.

The effects of glycerol on cochlear blood flow and serum osmotic pressure were studied in healthy guinea pigs. Laser Doppler flowmetry of cochlear blood flow after the esophageal-gastric administration of 50% glycerol demonstrated a greater increase in blood flow for a longer time than with the intravenous infusion of 50% glycerol. The intravenous infusion of glycerol did increase systemic blood pressure, which changed partially in parallel with the change in cochlear blood flow. The change in systemic blood pressure after esophageal-gastric administration was slight. In another experiment designed to observe the changes in serum osmotic pressure after glycerol administration, the esophageal-gastric route also caused a greater and longer increase in serum osmolarity than intravenous infusion. The increase in cochlear blood flow after glycerol administration was thought to be due to an increase in the osmotic gradient between the blood in the cochlear vessels and the interstitial fluid, or to the high osmolarity of the blood itself. The possible mechanisms underlying local blood flow increase caused by high serum osmolarity are discussed. Systemic blood pressure increase induced by glycerol could be an influential factor for the cochlear blood flow increase during intravenous infusion.